The present invention relates to a process for treating the surface of a plastic article, especially an article made of a polyolefin, in particular polypropylene or polyethylene. The invention also relates to a correspondingly treated plastic article.
In particular, the treatment of surfaces of plastic articles made from polymers of nonaromatic hydrocarbons meets with considerable difficulties. In order to enable such plastics to be lacquered or painted, priming is necessary. It is known to effect such a priming with polyester resins dissolved in xylene or ethylbenzene. These solvents incipiently dissolve the surface of the plastic component and thus permit adhesion of the polyesters via secondary valences. However, the solvents are highly toxic, so that their processing raises problems.
A different treatment of the surface of plastic components is carried out on plastic containers for motor fuel. Fuel containers of polypropylene or polyethylene are also particularly suitable, especially for unleaded gasoline types, since fuel containers of metal experience considerable disadvantages because of the corrosive nature of the unleaded fuels.
Without a surface treatment, however, the plastic containers allow an unduly high diffusion of fuel vapors. This diffusion cannot be tolerated for reasons of pollution of the environment and because of the losses of fuel. In a known technique, the inner surfaces of the fuel containers are therefore sulfonated by means of gaseous sulfur trioxide, whereby the surface of the tank is rendered hydrophilic and thus prevents diffusion of the fuel. Another process for reducing diffusion consists in fluorinating the container. However, this process has not yet been industrially proven.
Both sulfonation and fluorination of the fuel containers have the disadvantage that substances are used which are aggressive and injurious to health, and furthermore the release of these substances into the environment must be prevented under any circumstances. Apart from the health hazard, the processes are very expensive and must be carried out under extensive safety precautions.